The present invention relates to a method for determining sleep stages of an examinee from biosignals detected by a biosignal detector, which is readily handled and can be routinely used.
A sleep state is often examined as an indicator for determining the health condition of an individual. It is well-known that sleep and health are closely associated. Health and sleep depth and quality of sleep during the night are closely associated with mood and vigor on the following day. Meanwhile, during periods of mental stress or sickness, comfortable sleep is not obtained because the depth of sleep and the transition pattern of sleep stages are changed.
During healthy sleep, non-REM sleep and REM sleep repeatedly appear at a constant interval after falling asleep. It has been known that sleep rhythm is disturbed during periods of sickness or mental stress. Therefore, it becomes possible to know the mental stress level and poor physical condition of examinees by monitoring sleep stages and their occurrence pattern while the examinees sleep.
In particular, the elderly often complain of a sleep state disorder such as shallow sleep, and have a problem in sleep quality. By examining the transition of sleep stages to understand sleep quality, it becomes possible to find ways of addressing the problem in sleep quality, and find measures to improve sleep quality.
A conventional method for examining sleep stages is a the method using a sleep polysomnogram (PSG). In the method using PSG, a significant amount of information can be obtained by estimating the activity of the cerebral nervous system during sleep from brain waves, myoelectric potential and eye movements. However, it is difficult to obtain natural sleep because the measurement is performed by mounting many electrodes on the face and the body of an examinee, and a period of several days to a week is required for growing accustomed to this method. Therefore, physical and bodily loads given to the examinee are extremely heavy, and further, it is necessary that this measurement is performed in a special facility such as a hospital by an expert who is familiarized with the handling. Therefore, the cost required for this method becomes expensive.
Due to these circumstances, although it can be an effective therapy to use PSG for patients with an obvious sleep disorder, it is difficult to use PSG for routine health care.
Thus, methods for simply examining sleep stages without using PSG for examining the daily health state of the examinee have been proposed. For example, a method for determining the sleep stages by wearing a wristwatch type vibration strength measurement device on an arm and measuring its acceleration is available, but only two sleep stages, e.g., REM sleep and non-REM sleep can be detected. For health care use, however, it is necessary to detect at least three stages, i.e., the awake/REM sleep stage, the shallow non-REM sleep stage and the deep non-REM sleep stage. Thus, because this type of non-PSG device only detects two sleep stages, it is unsuitable for purposes of health care.
Another proposed method for determining sleep stages is a method for non-invasively measuring a heartbeat rate, and determining sleep stages from the measured heartbeat rate signal data (e.g., see Japanese Published Unexamined Patent Application 2000-325315). This method is capable of examining four sleep stages, e.g., the awake state, REM sleep, shallow non-REM sleep and deep non-REM sleep. Therefore, it is possible to use this method for health care. However, complicated calculations, calculation time and large memory are required because the sleep stages are determined by extracting heartbeat signals from non-invasively detected biosignals and analyzing the effect of the autonomic nerve from the heartbeat signals. As a result, the configuration of the device implementing this method becomes complicated, the device becomes more expensive, and thus, it is difficult to routinely use the device.
Thus, the present invention aims at providing a method for determining the sleep stages, which is readily handled even by the elderly and can be routinely used without physically or mentally burdening an examinee.
Furthermore, the present invention aims at providing a device realized by the method of the present invention, which is inexpensive in terms of price and maintenance costs and is readily introduced.